This invention relates to a liquid chromatograph, and more particularly to a conventional liquid chromatograph of the type shown in FIG. 4 which includes a solvent tank 1, a pump 2, a sample injection element 3, a column 4, a detector 5, and a recycle cock 6 for recycling solvent leaving the detector 5 back to the detector as a reference solution or exhausting the solvent into a waste tank 7.
In such a conventional liquid chromatograph it is difficult to flow in flowing the solvent at a minutely fixed flow rate and, therefore, it is hard to maintain a high stability of the measured value. This problem becomes revealed particularly when a highly sensitive detector is used or when a volatile solvent such as tetrahydrofuran or the like is used. In this regard, experience has shown that a high stability can be obtained when the solvent flows at a minutely fixed flow rate. At the same time, a greater flow rate of the solvent increases waste consumption of the solvent uneconomically. In addition, the solvent (reference solution) is easily affected by thermal influence in the detector, and a stable baseline cannot be obtained because drift is caused by thermal expansion of the reference solution. Moreover, when a minutely fixed flow rate of the solvent is not maintained, fluctuation of retention time (time until a measured value is reported) prevents accurate measurement and such inconvenience is caused that the measured value cannot be subjected to computer-processing.